When Deidre Ramos moved with her infant son to the Parker Street section of New Bedford, Mass., little did she know that her new neighborhood was toxic.

Today, a decade later, Ramos is worried about the health of her two sons growing up in a community still contaminated by an old burn dump containing polychlorinated biphenyls (PCBs).

“What will be the long-term effects on my children?” asked Ramos.

Now new research conducted in New Bedford suggests that these industrial chemicals, which were first linked to learning problems in children more than two decades ago, may play a role in attention-deficit hyperactivity disorder (ADHD), too.

Boys who were exposed to higher levels of PCBs in the womb scored lower on focus and concentration tests, which indicates they are more likely to have attention problems often related to ADHD, according to a newly published study of New Bedford area children.

All of the children studied were born to mothers who lived near the contaminated harbor and dumpsites in these low-income communities, where twice as many people live below the poverty line than the Massachusetts average. But experts say that their exposures were fairly low, comparable to children's levels throughout much of the United States, which means that a connection between PCBs and attention problems in boys could exist in other communities, too.

Banned in the United States more than 30 years ago, PCBs are long-lived industrial chemicals that accumulate in food chains. Nearly every U.S. resident still has detectable levels in his or her blood. PCBs have the ability to disrupt hormones, which can alter how the brain develops.

“These findings contribute to a growing literature showing associations between PCBs and ADHD-related behavior,” the scientists from Boston University, Harvard University and two other institutions wrote in the study, which was published in late February.

In the study, umbilical cord was collected from 788 newborns from four towns near New Bedford Harbor to see what they were exposed to in the womb. They were born between 1993 and 1998.

Blood from the umbilical cord “is one of the best measures of contaminants being transferred from mother to fetus,” said Sharon Sagiv, lead author of the study and an epidemiologist who now works at Boston University.

Roughly eight years after they were born, almost 600 of these children underwent two tests. One measured their ability to zero in on and react to a specific target — in this case, the image of a cat on a computer screen — and to inhibit their response to another animal's image. The other exam included parts of an IQ test that measured their processing speed and distractability, which tests whether they can maintain attention over time.

“It’s like playing whack-a-mole versus watching a radar monitor,” said Paul Eubig, a neuroscientist at the University of Illinois at Urbana-Champaign. Eubig, who studies effects in lab animals, was not involved in the study but co-authored a published report linking PCBs with changes related to ADHD.

Boys exposed to the highest levels of PCBs during their mother’s pregnancy failed to press a button for the on-screen cat 12 percent more often than children exposed to the lowest levels, according to the study published in the journal Environmental Health Perspectives. Those same boys also scored slightly lower in the other test.

The same link was not found in girls. Animal data suggest that hormone-disrupting chemicals including PCBs affect each gender differently, but the connection in humans remains unclear.

“It’s possible that these compounds can impact brain development by altering the hormonal balance of a developing fetus,” said Joe Braun, an epidemiologist at the Harvard School of Public Health who did not participate in the research. “Boys and girls have different hormonal patterns,” he said.

Boys are two to three times as likely as girls to develop ADHD, the most common learning disorder reported in children worldwide. In 2007, U.S. parents reported that nearly 10 percent of children between the ages of 4 and 17 had been diagnosed with ADHD, according to the Centers for Disease Control and Prevention.

The researchers in their report called the effect of PCBs on attention skills “modest.” But they noted that the links were strongest for the children’s errors of omission and variability in reaction times, which they called “indicators of inattention.”

In their findings, the scientists took into account other factors that may contribute to ADHD-related behaviors, such as whether the mother smoked during pregnancy. However, they cannot rule out that chance — or some other factor — did not contribute to the results.

In the study, 31 percent of the children were non-white, 24 percent of the fathers did not finish high school and 20 percent had an annual household income of less than $20,000 per year.

The authors reported that PCB levels in the New Bedford area infants “were low relative to other population-based studies, given maternal residence adjacent to the PCB-contaminated New Bedford harbor.”

Even for those with the highest exposures, the levels in the babies “were not remarkably higher than what we would expect to find in the general population,” said Jonathan Chevrier, an epidemiologist at the University of California, Berkeley, who has studied PCBs' effects in children living in an agricultural region of California.

Chevrier said this suggests New Bedford itself may not be the main source of contamination, but that PCBs found in cord blood may represent lifetime exposure in these women.

Other people with high exposures to PCBs include those in Great Lakes states, as well as populations near the Baltic Sea, in the North Atlantic and in the Arctic.

PCBs mostly come from eating fish, although meat and dairy also are sources. Digging or playing in PCB-laced soil or breathing in dust can also increase exposure.

In the mid 1980s, scientists first documented that PCBs had neurological effects in studies of Great Lakes children. Children of women who ate more contaminated fish from Lake Michigan performed more poorly on memory tests and other IQ tests than their peers. The same findings were reported among children from another Great Lakes region, Oswego, N.Y.

In New Bedford, PCBs, which were insulating fluids, were used to make electrical equipment at two plants from 1947 until 1977. They also were used as building materials.

Ramos’ neighborhood is part of the Parker Street hazardous waste site, approximately 114 acres that include two schools, homes and commercial properties built atop fill contaminated with PCBs from an old municipal burn dump.

City officials bought six residential properties within the site and built special caps and vapor-control systems at the schools. The U.S. Environmental Protection Agency and state have overseen removal of tainted soil, including work as recently as December, but some remains.

Also, less than a mile away, the harbor is one of the EPA’s largest Superfund cleanup sites. The EPA began removing contaminated soil from the harbor bottom in 2004, but officials predict the cleanup could take another 30 to 40 years.

Two high-ranking EPA officials are holding a town meeting in New Bedford on Tuesday to answer questions and address concerns of residents.

Now a member of the New Bedford-based environmental action group, CLEAN, Ramos, 32, has two sons, ages 7 and 10. They were born too late to participate in the study and neither of them has ADHD, although one has autism. There is no evidence linking PCBs and autism.

Ramos worries every day that living near the old dumpsite and the harbor could harm her boys.

“It’s a huge mess. I don’t even feel safe letting my kids play outside,” she said.